The objectives of the proposed research are to elucidate the role of matrix vesicles in the initiation of biological calcification. Effort is being made to characterize the matrix vesicles concerning mineral, protein, enzyme, lipid and other constituents. Other studies are being directed toward studying their metabolism relative to mineral formation, vesicle membrane synthesis and destruction. Special emphasis is being placed on the role of alkaline phosphatase and possible lipid-calcium-phosphate complexes in the de novo mineral formation by the matrix vesicles.